This invention relates to RF field generators and detectors, and more particularly to an RF field generator and detector for an NMR apparatus.
Heretofore, an RF field generator and detector of the specified type has been as shown in FIG. 8. Referring to the figure, numeral 1 designates an RF or high frequency coil, for example, saddle-shaped coil or solenoid coil, numerals 2 designates variable capacitors for impedance matching which are connected to the RF coil, and numeral 3 designates connection terminals which serve to couple the RF field generator and detector with an RF transmitter and receiver (not shown). Since the impedance of the RF coil 1 differs from the input and output impedances of the RF transmitter and receiver, the variable capacitors 2 function to match the impedance of the two.
FIG. 9 shows an example of the RF coil 1 which is used in the prior-art RF field generator and detector shown in FIG. 8. Numeral 4 indicates a copper wire which forms the RF coil 1, and to which electrodes 5 are connected. When the copper wire 4 is supplied with an RF current from the electrodes 5, an RF magnetic field 6 is produced.
The prior-art RF field generator and detector is constructed as described above. Therefore, in a case where it is operated with a comparatively high frequency above 25 MHz, especially above 40 MHz by way of example, the impedance of the RF coil increases, and relatively, the capacitances of the variable capacitors for impedance matching become too small, so that the construction of the RF field generator and detector is difficult. Besides, the breakdown voltages of the variable capacitors must be enhanced with the increase of the impedance of the RF coil, and this renders the variable capacitors large in size and high in price.